Software for die-stamping modelling

ABSTRACT

The invention concerns a method for digital simulation of a die-stamping process comprising the following steps: recording at least one metamodel consisting of a permanent collection of the digital representations of elementary components of die-stamping tools, each of the elementary components being defined in the form of finished elements, and comprising digital static attributes; recording a digital model for deforming a blank used in the process to be simulated; selecting a subassembly of the permanent collection, by temporarily recording the elementary components representing a particular die-stamping tool corresponding to the simulation concerned, the subassembly constituting a specific collection in the form of digitized finished elements of the specific collection, parameterizing said digitized finished elements of the specific collection, and the corresponding attributes based on the characteristics of the process to be simulated; recording the digital data representing the relative movements of the components of the specific collection, based on operating cycles of the die-stamping process to be simulated; recalculating the digital models for deforming the blank based on the recorded digitized data in the parameterized specific collection, of the digital model of the blank, and of the specific displacements; generating a digital or visual representation of deformations of the blank by applying the recalculated digital model.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to the field of software for simulatingphysical phenomena.

The present invention relates more particularly to software forsimulating pressing.

(2) Prior Art

The prior art already knows, through the American patent applicationU.S. Pat. No. 5,379,227 (Ford Motor), a method and system for evaluatingsheet metal forming tooling design, for use with a draw die including apunch and binder designed to form the sheet metal into a part, utilizingimproved implicit time integration methods that reduce numericalinstability, thereby enhancing convergence of numerical solutions. Thesheet metal and tool surface of the punch are each represented as a meshhaving a plurality of nodes. Contact nodes between the sheet metal meshnodes and the tool surface mesh can be identified. A first embodimentincludes minimizing discontinuities generated by unloading bydetermining a stress increment of a sampling point in the sheet metalmesh according to an incremental deformation theory of plasticity. Asecond embodiment includes modelling a draw-bead as a plurality ofnonlinear elastic springs to minimize discontinuities in the springforce during unloading. A third embodiment includes filtering a relativevelocity vector of at least one contact node with respect to the toolsurface, to avoid frictional force oscillations due to the change indirection of the relative velocity vector during formation of the part.

The prior art also knows, through the American patent application U.S.Pat. No. 5,552,995 (The Trustees of the Stevens Institute ofTechnology), a computer-based engineering design system to design apart, a tool to make the part, and the process to make the part. Thedesign system has a processor and a memory. The memory stores featuretemplates, each feature template being a representation of a primitiveobject having a form and a function. Each feature template is indexed bythe function of the primitive object and includes a representation of aprimitive geometric entity having the form of the primitive object. Eachfeature template can include information relating to a tool to make theprimitive object and a process to make the primitive object. The designsystem also includes an input device for receiving a request to designthe part. This request includes one or more predetermined functions thatthe part performs. A core design module, executable by the processor,designs the part, the tool to make the part and process to make the partby accessing the plurality of feature templates in the memory to locateone or more primitive objects that perform the one or more predeterminedfunctions.

The prior art also knows, through the American patent application U.S.Pat. No. 6,219,055 (SolidWorks), a computer-based forming tool. Aforming tool is provided for manipulating a computer model, includingmechanisms for allowing a user to define a forming tool for creating aform feature of the model. Characteristics of the forming tool may bedefined so that the forming tool may be reused without the need toredefine its characteristics.

The prior art also knows a solution for the design of a fabricationmethod comprising steps of representing a workpiece as a plurality oftriangular finite elements, representing pressing tools withmathematical equations which typically comprise cubic polynomials,simulating deformation of the workpiece by the pressing tools with afinite-element model, the finite-element model being integratedexplicitly. The method can be implemented by an apparatus whichcomprises a memory device storing a program comprising computer-readableinstructions, and a processor that executes the instructions. After thedeformation of the workpiece has been simulated by the finite-elementmodel, the characteristics of the workpiece and of the pressing toolscan be modified in order to improve the final form of the worpiece.After the simulation by finite elements has produced an acceptable finalworkpiece form, an actual workpiece can be pressed with real tools basedon the simulation.

The pressing simulation software of the prior art has the drawback of insome cases being limited with regard to the possibility of finelydefining the type of pressing process, and in other cases, moreparameterisable, the drawbacks seen from the point of view of the finaluser, being lengthy and complex to implement having regard to themagnitude of the parameterising.

SUMMARY OF THE INVENTION

The present invention intends to remedy the drawbacks of the prior artby proposing a system which enables the user to define his own pressingprocess models and which enables this same user or another, once apressing process has been defined, no longer to have to carry outanything but a limited number of parameterisings for the pressingprocess model in question. Meta-models are defined for generatingdialogues dedicated to the specific press of a given user.

To this end, the invention concerns, in its most general acceptance, anumerical simulation method for a pressing process comprising the stepsconsisting of:

-   -   recording at least one meta-model consisting of a permanent        collection of numerical representations of the elementary        constituents of pressing tools, each of the said elementary        constituents being defined in the form of finite elements, and        comprising numerical static attributes,    -   recording a numerical model of deformation of a blank used in        the process to be simulated,    -   selecting a subset of the said permanent collection, for        temporary recording of elementary constituents representing a        particular pressing tool corresponding to the simulation in        question, the said subset constituting a specific collection in        the form of digitised finite elements,    -   parameterising the said digitised finite elements of the        specific collection, as well as the corresponding attributes        according to the characteristics of the process to be simulated,    -   recording numerical information representing the relative        movements of the components of the said specific collection,        according to the operating cycles of the pressing process to be        simulated,    -   recalculating the numerical models of deformation of the blank        according to the numerical information recorded on the one hand        in the parameterised specific collection, the numerical model of        the blank, and the specific movements on the other hand,    -   generating a numerical or visual representation of the        deformations of the blank by the application of the said        recalculated numerical model.

The selection step preferably modifies the state of the elementaryconstituents that are not pertinent with regard to the constituentsselected.

Advantageously, the method comprises a step of loading at least part ofthe parameterising information of the collection from an externalinformation medium.

According to a particular embodiment, the method comprises a step ofloading the model of the blank from an external information medium.

According to a variant, the method comprises a step of loading thenumerical representation of the said sub-set from an externalinformation medium.

According to another variant, the step of making up the specificcollection is implemented by the display of a graphical interface andthe recording of the information entered from the said graphicalinterface.

Preferably, the step of displaying a graphical interface comprises anoperation of personalising a prerecorded interface, this personalisationtaking account at least partly of the information coming from the priorsteps of the method.

Advantageously, several levels of use are defined, one of the levels ofuse, supervision, requiring a common generic parameterising defining toa great extent the pressing method concerned and the other, basic,levels of use, requiring no more than a partial parameterising,complementary and specific, benefiting from the previously performedparameterising of the supervision level.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the help of thedescription, given below purely by way of explanation, of one embodimentof the invention, with reference to the accompanying figures:

FIG. 1 depicts the performance of the method according to the invention;

FIG. 2 depicts the formation and processing of the meta-model in theform of a computer file;

FIG. 3 depicts the application as seen by the supervisor;

FIG. 4 depicts the application as seen by the final user.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The term “pressing process” includes the tools and the characteristics.Moreover, “attribute” means a physical and numerical characteristic. Thedeformation is often referred to as “forming” by persons skilled in theart.

The term “project” covers the complete computer file comprising all thedata having to be processed by the “solver”, the result of this latterprocessing constituting the complete simulation.

The meta-model has the structure of a computer file, which constitutes amajor part of the project. As described in FIG. 2, this meta-model isformed by the supervisor, and the latter therefore partially fills inthe project and leaves fields that the final user will give informationon by means of a graphical interface. The set consisting of themeta-model and the data added by the final user, thus constituting acomplete project, is thus created and will be processed by the “solver”.The supervisor chooses whether or not he must leave the final user tofill in a given parameter. Where a parameter is requested of the finaluser, a default value for this parameter is often supplied by thesupervisor.

The aim of the invention is to enable the users to define themselves themajor part of the pressing modelling process. The concept ofmacrocommands is divided into two distinct steps:

-   -   defining the macrocommands in accordance with the requirements        of the process (carried out by the supervisor)    -   applying the macrocommands by giving information on a restricted        number of parameters (performed by the final user).

The “supervisor” is the person who creates the graphical interfacerepresenting the macrocommand, the steps, the diagram of the process,the groups of tools, the default attributes of the process and theattributes which will be requested of the final user (as shown in FIG.3). The “final user” is the person who uses the macrocommand defined bythe supervisor, giving information on the following parameters (asdepicted in FIG. 4): link between the groups and the mesh objects,parameters that can be modified for each pressing project (clampingforce, pressing speed, friction, etc). The “group” is a specific type ofobject: blank, blank holder, die, punch, etc. A group is defined by itsrepresentation in the diagram and the kinds of specific attributesdirectly accessible in the context of the groups. From the point of viewof the supervisor, a group corresponds to an object (a component of thepress) seen by the final user. The attribute is the value correspondingto a property of a group (and therefore to objects). This may be afriction, a direction, a 2D curve, etc. A step is a period of timeduring which each object has only one kind of kinematics: movement,force. The complete simulation process must be divided into varioussteps, in accordance with the behaviour of each group. Each group isactive, or non-active, during each step. If a group is not active duringa step, its entities (nodes, elements, 3D curves) will not be taken intoaccount by the solver during the processing of this step. A “parameter”is a value which is common to various groups and/or which can bedemanded of the user when he wishes to apply the macrocommand. This maybe a floating value (friction, thickness), a direction, a property ofmaterial, an integer value (level of fineness, number of points), a 2Dcurve.

The macrocommand must be created by a user called the supervisor withinthe application. The supervisor does not need to load the project. Whena user loads a preprocessed module of a project, he needs to prepare theobjects and meshes necessary for the process. He then accesses a buttonon the macrocommand tool bar, chooses the macrocommand that he wishes toexecute, sets the “final user parameters” offered by the correspondingdialogue box and clicks on the “apply” button. The steps and theattributes of the objects will then be allocated automatically to theobjects. The processing of the project can be started immediately.

Certain macrocommands, such as the conventional processes (single- anddouble-action presses, etc) are supplied in advance in a macrocommanddatabase. The users can use them directly, duplicate them and/or modifythem in order to adapt them to their use.

Firstly, the macrocommand will be considered from the point of view ofthe supervisor. A graphics window makes it possible to manage thefunctions of creation, copying and deletion relating to themacrocommands. Three first boxes (“blank”, “tools” and “parameters”)contain data which will be active throughout the processing: thephysical attribute of the blank, the list of groups corresponding to thetools (with the group name, colour, material and thickness) and the listof the parameters of the final users. The list of the parameterscontains parameters which have two objectives: the first is, for thesupervisor, to locate in an isolated place a value which will be used byone or more group attributes (for example the tool/blank friction,common to all the principal tools). This simplifies the modification ofthis value. The second objective is to determine which parameters willbe requested of the final user. These parameters can be: properties ofmaterials, the friction, the thickness, the direction of the pressing,the speed curve, etc.

The main box (called “steps”) makes it possible to allocate attributesto each group for each step. With regard to the buttons for managing thesteps, one button per step updates the diagram, the active groups andthe attributes. The supervisor can add, duplicate or remove steps. Thediagram shows the relative positions of each group according to eachstep. Its use makes it possible to show diagrams of the steps of theprocess, showing the various tools, their kinematics and their state(active or not during the step).

A toolbox appears whenever the macrocommand editing window is called upin supervisor mode. This toolbox comprises four pages of the pattern ofthe pressing process: the “tools” page, the “blanks” page, the“behaviour” page and the “post-process” page.

The sections “blanks” and “tools” contain attributes that are common forall the steps (names of groups and colours, attributes of materials).

The pressing groups (blanks, tools, post-process, behaviour) representthe content of the steps. The groups of blanks must have a true hardwareattribute.

The invention is described above by way of example. Naturally a personskilled in the art is in a position to implement various variants of theinvention without for all that departing from the scope of the patent.

1-8. (canceled)
 9. A method for the numerical simulation of a pressingprocess comprising the steps consisting of: recording at least onemeta-model consisting of a permanent collection of numericalrepresentations of elementary constituents of pressing tools, each ofthe elementary constituents being defined in the form of finiteelements, and comprising numerical static attributes, recording anumerical model of deformation of a blank used in the process to besimulated, selecting a subset of the permanent collection, for temporaryrecording of elementary constituents representing a particular pressingtool corresponding to a simulation in question, the subset constitutinga specific collection in the form of digitized finite elements,parameterizing the digitized finite elements of the specific collection,as well as the corresponding attributes according to characteristics ofthe process to be simulated, recording numerical informationrepresenting relative movements of components of the specificcollection, according to operating cycles of the pressing process to besimulated, recalculating numerical models of deformation of the blankaccording to numerical information recorded on the one hand in theparameterized specific collection, the numerical model of the blank, andspecific movements on the other hand, and generating a numerical orvisual representation of the deformations of the blank by theapplication of the recalculated numerical model.
 10. A simulation methodaccording to claim 9, wherein the selecting step comprises modifying thestate of the elementary constituents that are not pertinent with regardto the selected constituents.
 11. A simulation method according to claim9, further comprising a step of loading, from an external informationmedium, at least part of the collection parameterizing information. 12.A simulation method according to claim 9, further comprising a step ofloading, from an external information medium, the model of the blank.13. A simulation method according to claim 9, further comprising a stepof loading, from an external information medium, the numericalrepresentation of the subset.
 14. A simulation method according to claim9, wherein the step of forming the specific collection further comprisesdisplaying a graphical interface and recording information captured fromthe graphical interface.
 15. A simulation method according to claim 14,wherein the step of displaying a graphical interface comprisespersonalizing a prerecorded interface, wherein said personalization atleast partly takes account of the information coming from the priorsteps of the method.
 16. A simulation method according to claim 9,further comprising defining several levels of use, with one of thelevels of use, supervision, requiring a common generic parameterizingdefining to a major extent the pressing method concerned and the other,basic, levels of use, basic, requiring no more than partialparameterizing, complementary and specific, benefiting from thepreviously performed parameterizing of the supervision level.